Not all oils are the same......
We have had some customers try using Chain Saw Oil but cant recommend it as it is just too sticky and glue like to flow properly at ambient temps up to 28°C. Besides which some Chainsaw oils are vegetable based - be aware some of these oils attack nitrile seals such as the O or X rings in your chain!
Lastly if you do go out to buy oil for your chain and can't get or dont want a bespoke chain oil, get some Gearbox oil, something like EP70/90 is fine if the ambient temp is warm enough! BUT....its no use using thick Gearbox oil where the ambient temperature is under 25°C, its just too thick and will only flow very slowly, for that reason we really dont recommend using 80/90 gear oil in the UK- here's hoping we have a summer that makes that possible!
Gearbox oil has got the sort of additives you need for a chain drive and it doesnt turn to a "water like" viscosity in hot weather (if you can't remember what "Hot weather" is do a Google seach on May 24th 2012 for the UK or southern Spain at almost any other date)
BUT please NEVER, EVER USE AUTOMATIC TRANSMISSION FLUID in your oiler!, some variants have all sorts of nasty toxins in and can destroy plastics, some even corrode brass!